Nowadays, some important issues in the BIM field and research are still open, and are not deeply known and really understood yet by all the BIM users and approaches; unfortunately, this critical situation implies, often, incorrect approaches and ineffective applications, especially using BIM for existing historical building, where the object oriented approach has so many limitations. In fact, the current laser scanning technology can detect just a cloud of points that is considered "non-intelligent" according to the BIM method and meaning. The paper presents an important case study: the Cathedral of Piazza dei Miracoli (Miracles Square) in Pisa. The method we propose consists of an innovative procedure combining in a two-way manner the correspondence levels between metrology and ontology of the constructive components. The paper proves that is not important to obtain the best possible level of modeling performance. We need a specific BIM approach, for “a specific building”, according with “a specific project”. We believe that it is precisely in this capacity of matching between metrological and constructive knowledge (mediated by computer graphics technology) that it is possible to identify the response to an important programmatic indication in the BIM field: "how much BIM?". This sentence was explained by Charles Eastman (recognized worldwide as the father of BIM) during his "lectio magistralis" at the Master BIM of the University of Pisa (www.unibim.it). We guess this is the way to be free from any pre-established intervention standards, and so to be adapting to a specific construction for a specific intervention’s level using specific resources.